There's no canonical answer for this, since branches are simply pointers to certain commits in a DAG. For instance, master and foo could be pointing at the same commit; if you then create a branch from foo, it's effectively the same as creating a branch from master.

That said, if you visualize the commit graph (via gitk or some other graphical history tool), you can get a general sense of where the branch points are in the commit graph, versus where various branch pointers are pointing.